At present, as a mobile wireless communication system as represented by a system for mobile phones, multiple access systems based on OFDMA (Orthogonal Frequency Division Multiple Access) which applies OFDM (Orthogonal Frequency Division Multiplexing) and SC-FDMA (Single Carrier Frequency Division Multiple Access) have been studied.
3GPP Specification TS36.211 V8.0.0 (2007-09) pp. 10-11, pp. 14-17, and 3GPP contribution TSG RAN1 #51 R1-074949 disclose techniques in which control is performed in a unit of time-frequency domain referred to as a resource block. The resource block is acquired by dividing the time into a plurality of time symbols and by dividing frequencies into a plurality of bands each of which is formed of a plurality of sub-carrier groups. Control is also performed in a unit of time domain referred to as a frame, which is formed by integrating a plurality of resource blocks in a time direction. By adopting these control methods, in which the control is performed in a unit of time-frequency domains or time domains, channel allocation and data transmission to a plurality of user terminals (mobile stations) can be performed efficiently.
A propagation path for a mobile wireless communication changes in time and frequency due to a spatial arrangement of antennas and obstacles, and a movement of a user terminal (a mobile station). Therefore, generally for data transmission, a reference signal, which is acquired by modulating a known sequence, needs to be transmitted and received between the user terminal (the mobile station) and a base station, to measure the propagation path for each band. The reference signal is used to obtain a transfer function of the propagation path of a channel that is used for data transmission, when data is demodulated.
Further, a reference signal is used when scheduling is performed to allocate channels to a plurality of user terminals (mobile stations), respectively. The reference signal is used for checking a state of a propagation path over a wide band of the respective user terminals (mobile stations) and for allocating a user in a good propagation path state in each frequency.
The latter reference signal is referred to as a sounding reference signal in 3GPP Specification TS36.211 V8.0.0, and 3GPP contribution TSG RAN1 #51 R1-074949, or the like, and is used in an uplink (mobile station for transmission and base station for reception). The sounding reference signal is a reference signal for selecting a frequency to be used for data transmission, and is different from the former reference signal for demodulating data in that it is transmitted and received in a wide band. In 3GPP Specification TS36.211 V8.0.0, a user terminal (a mobile station) transmits a sounding reference signal for all bands to a base station in a certain time symbol, to measure the propagation path state.
According to this method, when correlation of propagation paths between frequencies is high, the state of an uplink propagation path can be measured with respect to a plurality of user terminals (mobile stations) simultaneously. The user terminals use sounding reference signals of patterns orthogonal to each other. Improvement of frequency utilization efficiency can be performed by the scheduling technique mentioned above.
FIG. 7 shows an example of a time-frequency arrangement of the sounding reference signal in the conventional technique. A domain enclosed by a time width T and a frequency bandwidth F indicates a single resource block. In Nonpatent Literature 1, the time width of the resource block includes about ten symbols, and the frequency bandwidth of the resource block includes about ten or twenty sub-carriers. In the conventional technique, a sounding reference signal 4 is transmitted by using a single time symbol expressed by a shaded area over a bandwidth corresponding to resource blocks 1, 2, and 3. The number of the resource blocks in a frequency direction is three in FIG. 7; however, the value that can be taken in Nonpatent Literature 1 is from several to about a hundred, and also, such a case can be considered that a certain user terminal (a mobile station) transmits a sounding reference signal over a wide band. Also in this case, the user terminal (the mobile station) transmits a sounding reference signal in a determined time symbol in resource blocks.